As such a type of conventional clamp device, there is a clamp device disclosed in Patent Literature 1 (Japanese Laid-Open Patent Publication No. H08-177814). The clamp device of the conventional art is configured as follows.
A middle portion of a clamp arm in a longitudinal direction thereof is mounted on a housing (clamp arm receiving stand) via a fulcrum shaft so as to be swingable in an up-down direction. A leading end portion of the clamp arm is provided with an output portion (working point) which presses an object to be fixed, and a rear end portion of the clamp arm is provided with an input portion (power point) which is pressed up by a piston.
A first hole for mounting a spring is formed at the leading end side of the housing so as to be opened obliquely upward toward a leading end-adjacent portion of the clamp arm. In addition, a second hole for mounting a spring is formed at the leading end side of the clamp arm so as to be opened obliquely downward toward the first hole. A return spring for returning the clamp arm is installed in the first hole and the second hole.
In fixing the object to be fixed by means of the conventional clamp device, a pressure fluid is supplied into a working chamber located at the lower side of the piston. Accordingly, the input portion of the clamp arm is pressed up by the piston, the clamp arm swings, and the output portion presses the object to be fixed. In this lock state, the return spring is compressed between the housing and the clamp arm.
In return-driving the clamp device from the lock state to a release state, the pressure fluid in the working chamber is discharged therefrom. Accordingly, the output portion of the clamp arm is pressed up by a biasing force of the return spring, and the input portion of the clamp arm presses down the piston. Thus, the lock state of the object to be fixed is released.
[PTL 1] Japanese Laid-Open Patent Publication No. H08-177814